In the process of manufacturing steel, iron and steel scrap is typically produced. The iron and steel scrap is an important material that can be used in high-quality steel and cast iron products and so the iron and steel scrap needs to be recycled. Unfortunately, much of the available iron and steel scrap, in particular those produced in automobile manufacturing, is contaminated with residual impurity elements such as copper and tin. Such impurities prevent the use of steel scrap directly for such higher-quality steel products.
Many impurities are commonly found in steel scrap. Of those impurities, copper (Cu) is typically cited as the most harmful because it can limit the end uses of the steel scrap. For example, excessive copper levels can cause problems in process that use the steel scrap, e.g., severe surface cracking during hot rolling (hot shortness), inhibit recrystallization during hot forming, and reduce ductility in deep drawing.
It is estimated that quality of steel scrap will deteriorate markedly over the next decade largely due to the increasing copper content. At the same time, the demand for high quality steel scrap will continue to increase. These trends are occurring because of the increased recycling and decreased production of home scrap. As well, the growth of electric arc furnace steelmaking and the decreasing quantities of home scrap in the major integrated producers have led to a greater demand for quality scrap and increased copper impurity levels. Further, with the ongoing acceleration of the production of sheet steel by minimills, high-grade scrap is likely to become scarcer and more expensive.
For these reasons, considerable effort has been made to develop a technology for the removal of copper from steel (or ferrous) scrap during the last decade. A number of technologies have been identified and attempted for the removal of copper from either ferrous scrap, whether in liquid or solid form.
Unfortunately, the best of these known processes for removal of copper (as well as Sb, As, Pb, and Zn) and Cu were those methods including selecting scrap and mechanical element cleaning. But such methods have several drawbacks, such as low efficiency and environmental concerns.